Method and system for enhanced oil recovery

ABSTRACT

A system and method for gas injection enhanced oil recovery is disclosed herein. The method includes the step of burning solid fuel and an oxygen-bearing gas in a combustion chamber. The method also includes the step directing an output stream of the burning step through a fluid pathway extending from the combustion chamber and underground to push oil toward a well. The method includes the step maintaining the pressure in the combustion chamber above ambient during the burning step.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a gas injection method for enhanced oil recovery.

2. Description of Related Prior Art

Enhanced oil recovery is a term for techniques applied to increase the amount of crude oil that can be extracted from an oil field. Through enhanced oil recovery techniques, 30-60% or more of the reservoir's original oil can be extracted compared with 20-40% using primary and secondary recovery methods. Enhanced oil recovery is also referred to as improved oil recovery or tertiary recovery. Enhanced oil recovery is achieved by gas injection, chemical injection, ultrasonic stimulation, microbial injection, or thermal recovery such as cyclic steam, steamflooding, and fireflooding. Gas injection is presently the most-commonly used approach to enhanced oil recovery. A gas, such as carbon dioxide or natural gas or nitrogen, is injected into the oil-bearing stratum under high pressure. The pressure of the gas pushes the oil toward the production well and assists in driving the oil up to the surface. In addition to providing a source of driving-pressure, the gas can also mix with the oil and thereby reduce the viscosity of the oil.

SUMMARY OF THE INVENTION

In summary, the invention is a system and method for gas injection enhanced oil recovery. The method includes the step of burning solid fuel and an oxygen-bearing gas in a combustion chamber. The method also includes the step directing an output stream of the burning step through a fluid pathway extending from the combustion chamber and underground to push oil toward a well. The method includes the step maintaining the pressure in the combustion chamber above ambient during the burning step.

BRIEF DESCRIPTION OF THE DRAWING

Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 is a simplified schematic of a system according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Referring now to FIG. 1, a system 10 according to an exemplary embodiment of the invention includes a combustion chamber 12 operable to contain solid fuel and an oxygen-bearing gas while burning at a pressure maintained above ambient. The system 10 also includes a fluid pathway 14 extending from the combustion chamber 12 and underground 16 for directing an output stream of the combustion chamber 12 to push underground oil toward a well 18.

The exemplary system 10 can also include a sub-system for power generation. A thermal fluid such as water can travel along a closed-loop fluid circuit 20. A condenser 22, a pump 24, a heat exchanger 26, and a steam turbine 28 can be positioned along the fluid circuit 20. Thermal fluid in liquid state can be pumped by the pump 24 to the heat exchanger 26. The thermal fluid can extract thermal energy from the output stream of the combustion chamber 12 to change to vapor state. A portion 30 of the fluid pathway 14 can pass through the heat exchanger 26. The thermal fluid in vapor state, such as steam, can move from the heat exchanger 26 and pass across the steam turbine 28. The energy of the thermal fluid can be extracted and converted to rotation by the steam turbine 28. The steam turbine 28 can transmit rotational power to other components, such as a rotor of a generator 32. The generator 32 can generate electricity in response to the input of rotational power from the steam turbine 28. It is noted that rotational power can be transmitted directly from the steam turbine 28 or through intermediary structures, such as a transmission or clutch. It is also noted that the steam turbine 28 can transmit rotational power to structures other than the generator 32. After passing across the steam turbine 28, the thermal fluid can pass through the condenser 22 and return to liquid state.

As set forth above, solid fuel and an oxygen-bearing gas can be burned at a pressure maintained above ambient in the combustion chamber 12. In the exemplary embodiment, the solid fuel can be coal. Any kind of coal can be used in practicing various embodiments of the broader invention. The coal can be of relatively high or relatively low carbon content. The coal can be of relatively high or relatively low sulfur content. Burning coal having a higher sulfur content can result in the production of carbon disulfide, which can be helpful in thinning the underground oil. Thinning the oil can be helpful in promoting oil recovery.

The solid fuel can be directed to the combustion chamber 12 with a solid fuel handler 34, shown schematically. The solid fuel handler 12 can be a device, or a plurality of devices working together, operable to receive the solid fuel and deliver the solid fuel to the combustion chamber 12 in a desired form. For example, if coal is used as the solid fuel, the solid fuel handler 34 can be operable to deliver coal to the combustion chamber 12 in powder form. The solid fuel handler 34 can include a pulverizer to reduce the size of individual pieces of solid fuel. The solid fuel handler 34 can also include devices for containing the solid fuel such as hoppers and/or also include devices for moving the solid fuel such as conveyors from a railroad receiving station and/or injectors projecting into the combustion chamber 12. The device or devices of the solid fuel handler 34 can be supplied with rotational or mechanical power directly or indirectly from the steam turbine 28, or can be supplied with electrical power from the generator 32. It is noted that the dashed lines in FIG. 1 represent paths for the transmission of electrical power.

The oxygen-bearing gas delivered to the combustion chamber 12 can be pure oxygen or air. The nature of the output stream will be affected by the properties of the solid fuel and the properties of the oxygen-bearing gas. When pure oxygen is the oxygen-bearing gas and desulfurized coal are burned together, the output stream can be substantially pure carbon dioxide. Carbon dioxide is miscible in oil and can therefore be helpful in promoting oil recovery. As set forth above, when the coal includes sulfur, carbon disulfide can be a component of the output stream. When air is the oxygen- bearing gas and untreated coal is the solid fuel, the output stream can include carbon dioxide, nitrogen, water, ash, as well as trace amounts of other gases. All of these components can be directed underground. Alternatively, one or more of these components can be separated from the rest of the output stream before the remainder of the output stream is directed underground.

The system 10 can include an oxygen separator 36 on site with the combustion chamber 12 for separating oxygen from air and delivering substantially pure oxygen to the combustion chamber 12. The oxygen separator 36 can apply any process for oxygen separation. For example, cryogenic air separation can be applied. U.S. Pat. No. 6,279,344 is hereby incorporated by reference as one example of a cryogenic air separation method in which a stream of oxygen is generated. Another process for separating oxygen from air or generating an oxygen stream occurs in a solid oxide fuel cell. Air can be pressurized to around 300 p.s.i. and injected into a fuel cell. Electric current can be passed through the cell to generate a stream of oxygen. U.S. Pat. No. 7,531,260 is hereby incorporated by reference as one example of a solid oxide fuel cell that can be applied in embodiments of the invention. The oxygen separator 36 can be supplied with rotational or mechanical power directly or indirectly from the steam turbine 28, or can be supplied with electrical power from the generator 32.

The oxygen generated by the oxygen separator 36, or any other oxygen-bearing gas directed into the combustion chamber 12, can be compressed by a compressor 38. The compressor 38 can also compress air directed to the oxygen separator 36. The compressor 38 can be operable to compress the oxygen-bearing gas to between 200 p.s.i. and 3000 p.s.i. in various embodiments of the invention. Some embodiments of the broader invention can be practiced wherein the range of pressure is 1500-2500 p.s.i. Other embodiments of the broader invention can be practiced over different ranges. The combustion chamber 12 is operable to contain the solid fuel and the oxygen-bearing gas while the combination is burned at a predetermined pressure above ambient or while burning over a pressure range. The compressor 38 can be supplied with rotational or mechanical power directly or indirectly from the steam turbine 28, or can be supplied with electrical power from the generator 32.

The combined solid fuel and oxygen-bearing gas can be burned in the combustion chamber at a pressure of between 200-3000 p.s.i. and at a peak temperature of between 4500° F.-6000° F., outlet temperatures will be between 100 and 4000 F. Because the combined solid fuel and oxygen-bearing gas are burned together under elevated pressurize, the combustor chamber 12 can be about 1/100 of the size of a combustion chamber currently used in enhanced oil recovery systems. This benefit can be enjoyed because, generally, a heat transfer coefficient of the output stream changes with changes in pressure. As the pressure during combustion increases, the heat transfer coefficient increases so that more energy can be extracted at the heat exchanger 26. Another benefit that can be enjoyed from higher-than-ambient pressure combustion is that the heat exchanger can be about 1/40 of the size of a heat exchanger currently used in coal fired power plants.

As set forth above, ash can be a portion of the output stream of combustion. If the ash does not clog the fluid pathway 14 or otherwise hinder oil recovery, the ash can be directed underground with the gases generated by combustion. However, the system 10 can also include ash handling equipment, represented schematically at 40 in FIG. 1. The ash handling equipment 40 is shown positioned between portions 42, 44 of the fluid pathway 14, but the ash handling equipment 40 could be positioned at another location in alternative embodiments of the invention. The ash handling equipment 40 could be an electrostatic precipitator or could remove ash by another process. The ash handling equipment 40 can be supplied with rotational or mechanical power directly or indirectly from the steam turbine 28, or can be supplied with electrical power from the generator 32.

The system 10 can include a recirculation pathway 46. A portion of the output stream of combustion can be returned to the combustion chamber 12 after the output stream has passed the ash handling equipment 40 and the heat exchanger 26. In an embodiment of the invention, seventy-five percent (if nearly pure O2 is the oxidizing stream input to the coal combustor, or approx 0-30% if the oxidizing stream is air) of the output stream can be directed back to the combustion chamber. However, in another embodiment of the invention, the recirculation pathway 46 can be omitted and all of the output stream can be directed underground. The recirculation pathway 46 is shown extending from a portion 52 of the fluid pathway 14, but the recirculation pathway 46 could extend from another position along the fluid pathway 14 in alternative embodiments of the invention.

The system can include a compressor 48 downstream of the combustion chamber 12. In some embodiments of the invention, compression of the output stream can be desirable. For example, if the output stream is compressed, the oxygen-bearing gas can be directed into the combustion chamber 12 at a lower pressure and the combustion chamber 12 can be less robust. However, it is noted that the invention can be practiced without a compressor downstream of the combustion chamber 12. The compressor 48 can be supplied with rotational or mechanical power directly or indirectly from the steam turbine 28, or can be supplied with electrical power from the generator 32.

Another basis for compressing the output stream can be that more energy can be extracted from the output stream at the heat exchanger 26. The output stream can enter the heat exchanger 28 at a temperature of between 4500° F.-6000° F. and a pressure of between 200-3000 p.s.i. The output stream can exit the heat exchanger 26 at a temperature of between 200° F.-1000° F. (approximately 3% -25% of the combustion temperature in the exemplary embodiment) and a pressure of between 160-2400 p.s.i. (approximately 80% -100% of the combustion pressure in the exemplary embodiment). The amount of energy extracted, or the rate of energy extraction, from the output stream can be selected based on the power needs of the system 10. For example, if the system 10 includes the oxygen separator 36, the solid fuel handler 34, the compressor 38, the ash handling equipment 40, and the compressor 48, more power can be extracted than if the system 10 only includes the compressor 38. If the energy extracted from the output stream to power accessories causes the pressure to drop below an amount desired for oil recovery, the system 10 can include the compressor 48.

The amount of energy extracted can be greater than the amount of power needed to power the system 10. For example, the operator of the system 10 can choose to generate power in excess of the needs of the system 10 and can then sell the excess power to a customer, referenced at 50 in FIG. 1. Thus, embodiments of the invention can be practiced wherein the operator of the system is a power supplier rather than a purchaser of power.

Another aspect of the operation of the system 10 is the temperature of the output stream at entry into the ground. The operator of the system 10 can direct the output stream into the ground at relatively higher temperatures or at relatively lower temperatures. For example, a higher temperature will exacerbate thinning of the oil and thereby promote oil recovery. However, on the other hand, higher temperatures could increase the cost of injection piping since larger and more robust piping may be required. Generally, it can be more desirable in at least some embodiments of the invention to emphasize higher pressures rather than temperatures. It can be desirable to have the output stream in the state of a supercritical liquid since it will be easier to pump underground and will impart more pressure urging movement of the oil.

A portion 54 of the exemplary fluid pathway 14 extends from the compressor 48 and extends underground. The output stream of combustion can be injected underground at one or more locations in embodiments of the invention. It is noted that U.S. Pub. No. 2008087425 and U.S. Pat. Nos. 5,065,821 and 5,803,171 are incorporated by reference as exemplary teachings of how the output stream, or a portion of the output stream, can be applied to move oil. Other injection schemes can be applied in embodiments of the invention.

It is also noted that the system 10 can include a central controller to control the operation of the individual components of the system.

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. The right to claim elements and/or sub-combinations of the combinations disclosed herein is hereby reserved. 

1. A gas injection method for enhanced oil recovery comprising the steps of: burning solid fuel and an oxygen-bearing gas in a combustion chamber; directing an output stream of said burning step through a fluid pathway extending from the combustion chamber and underground to push oil toward a well; and maintaining the pressure in the combustion chamber above ambient during said burning step.
 2. The gas injection method of claim 1 wherein said burning step is further defined as: burning solid fuel and substantially pure oxygen in the combustion chamber.
 3. The gas injection method of claim 1 wherein said directing step is further defined as: directing all of the output stream of said burning step underground.
 4. The gas injection method of claim 3 wherein said directing step is further defined as: directing all of the output stream of said burning step underground without compressing the output stream subsequent to said burning step.
 5. The gas injection method of claim 1 wherein said directing step is further defined as: directing the output stream of said burning step underground with the pressure of the output stream being between substantially eighty percent and substantially ninety-nine percent of the pressure of the combustion chamber when the output stream moves below ground level.
 6. The gas injection method of claim 1 wherein said directing step is further defined as: directing the output stream of said burning step underground while a temperature of the output stream is between substantially three percent and substantially ninety percent of a temperature of the combustion chamber when the output stream moves below ground level.
 7. The gas injection method of claim 1 wherein said directing step is further defined as: directing the output stream of said burning step underground to push oil toward a well without compressing the output stream downstream of the combustion chamber.
 8. The gas injection method of claim 1 wherein said maintaining step is further defined as: maintaining the pressure in the combustion chamber between 200-3000 pounds per square inch (p.s.i.) during said burning step.
 9. The gas injection method of claim 1 further comprising the step of: extracting energy from the output stream of said burning step prior to the output stream moving underground during said directing step.
 10. The gas injection method of claim 9 wherein said extracting step is further defined as: extracting thermal energy from the output stream of said burning step without causing a significant pressure drop in the output stream whereby additional compression of the output stream is required prior to the output stream moving underground.
 11. The gas injection method of claim 9 further comprising the steps of: creating steam with the thermal energy extracted during said extracting step; and passing the steam across a steam turbine to produce power.
 12. The gas injection method of claim 11 wherein said maintaining step further comprises the steps of: compressing the oxygen-bearing gas to a first level of pressure with a compressor prior to said burning step; at least substantially keeping the pressure of oxygen-bearing gas at the first level of pressure during said burning step; and coupling the compressor and the steam turbine such that the steam turbine powers the compressor.
 13. The gas injection method of claim 11 further comprising the steps of: separating oxygen from air with an oxygen separator on site with the combustion chamber; and delivering the separated oxygen to the combustion chamber.
 14. The gas injection method of claim 11 further comprising the steps of: pulverizing the solid fuel with a pulverizer; delivering the pulverized solid fuel to the combustion chamber with a conveyor; and powering the pulverizer and the conveyor with at least a portion of the power produced during said passing step.
 15. The gas injection method of claim 11 further comprising the steps of: removing ash from the output stream with ash removal equipment; and powering the ash removal equipment with at least a portion of the power produced during said passing step.
 16. The gas injection method of claim 11 further comprising the steps of: compressing the oxygen-bearing gas to a first level of pressure prior to said burning step with a compressor; providing oxygen to the combustion chamber with an oxygen separator on site with the combustion chamber; delivering the pulverized solid fuel to the combustion chamber with a solid fuel handler; and powering the compressor, the oxygen separator, and the solid fuel handler with at least portions of the power produced during said passing step, wherein the energy extracted during said extracting step to produce power delivered during said powering step is limited such that the output stream does not require compression downstream of the combustion chamber.
 17. The gas injection method of claim 9 wherein said extracting step is further defined as: extracting energy from the output stream of said burning step prior to the output stream moving underground during said directing step such that an amount of energy extracted is in excess of that needed to carry out said maintaining and directing steps.
 18. The gas injection method of claim 9 wherein said extracting step is further defined as: extracting energy from the output stream of said burning step prior to the output stream moving underground during said directing step such that an amount of energy extracted is in excess of that needed to carry out said maintaining and directing steps and wherein the amount of energy extracted is limited such that the output stream does not require compression downstream of the combustion chamber before moving underground.
 19. A system for gas injection method of enhanced oil recovery comprising: a combustion chamber operable to contain solid fuel and an oxygen-bearing gas while burning at a pressure maintained above ambient; and a fluid pathway extending downstream of the combustion chamber and underground for directing an output stream of the combustion chamber underground to a push oil toward a well.
 20. The system of claim 19 further comprising: a heat exchanger disposed along the fluid pathway and operable to extract heat from the output stream; a steam turbine; a fluid circuit including said heat exchanger and said steam turbine wherein a heat transfer fluid passing through said fluid circuit absorbs heat in said heat exchanger to become steam and then passes across said steam turbine; a compressor operable to pressurize the oxygen-bearing gas prior to the oxygen-bearing gas passing into said combustion chamber, wherein said compressor is powered by said steam turbine; and an oxygen separator powered by said steam turbine and operable to generate substantially pure oxygen to said compressor. 